For a long time, the aim in technology has been to use the rays of atom clusters, in particular with ionized and electrically accelerated clusters for thin layer deposition (T. Tackagi, I. Yamada, M. Kunoi, S. Kobiyama, Proceedings of the Second International Conference on Ion Sources, Vienna 1972, pages 790-796; DP-AS 25 47 552).
Compared to rays from single atoms, cluster beams deliver higher mass flow densities, in particular also of accelerated ionized clusters, and produce an especially intimate connection to the substrate even at a low substrate temperature when the kinetic energy of bombardment is appropriate.
A vapor-coating system is known from DP-AS 245 47 522, where the material to be deposited is heated and evaporated in a crucible, which is closed except for a nozzle opening, in a high vacuum, in order to cool on the basis of adiabatic expansion when ejected from the nozzle and to condense into atom clusters. It can be inferred from DP-PS 26 28 366, line 35, or DP-PS 3502902, line 45, that a nozzle admission pressure of about 10.sup.-2 hectopascals up to a few hectopascals is used in the crucible.
However, more recent studies of beams produced with corresponding, also commercially available systems, have clearly shown that these beams contain virtually no detectable portion of clusters with more than about 25 atoms. (W. L. Brown, M. F. Jarrold, R. L. NcEachern, N. Sosnowski, G. Takaoka, H. Usui, I. Yamada, Nuclear Instruments and Methods in Physics Research, volume B59/60, 1991, pages 182-189; D. Turner, H. Shanks, Journal of Applied Physics, volume 70, 1991, pages 5385 to 5400). Therefore, the effects of ionization and acceleration of such rays on the deposited layer should stem only from ionized single atoms. It is also in keeping with the fact that the targeted coating rates are only in the range of 0.1 nm layer thickness per second and thus also correspond to the coating rates that can be obtained with conventional molecular ray epitaxy.